1. Field of the Invention
The invention relates to an image reading apparatus for reading an image formed on a sheet, and particularly to an image reading apparatus for reading an image on a sheet without shifting the position of the sheet placed on a reading glass member, and an image forming apparatus provided with the image reading apparatus.
2. Description of Related Art
There has heretofore been an image forming apparatus provided with an image forming portion, an image reading portion and a document feeding apparatus or the like for supplying sheets (hereinafter referred to as the “documents” having images formed thereon one by one to the reading position of the image reading portion and discharging the documents after read to a document discharge stand, like a digital copying machine, a facsimile apparatus, a printer or a compound machine of these.
Image forming apparatus have heretofore included, for example, an image forming apparatus according to a first conventional example shown in FIGS. 9 to 12 of the accompanying drawings, and an image forming apparatus according to a second conventional example (e.g. Japanese Patent Application Laid-Open No. Hei 10-293431) shown in FIGS. 13 to 19 of the accompanying drawings.
(Image Forming Apparatus According to the First Conventional Example)
The image forming apparatus 100 according to the first conventional example is provided with an image forming portion 101, an image reading portion 102 and a document feeding portion 103. The image reading portion 102 and the document feeding portion 103 together constitute an image reading apparatus 120.
The image reading portion 102 is adapted to read an image by two methods, i.e., a “flow-reading mode” for fixing a reading sensor 104 at a predetermined position, and reading an image while transporting a sheet-like document P1 by the document feeding portion 103, and a “fixed-reading mode” for fixing a thick document such as a book on a document glass stand 105, and reading an image while moving the reading sensor 104 in the directions of double-headed arrow A.
The “flow-reading mode” will first be described. The documents P1 stacked on the document tray 106 of the document feeding portion 103 are fed out by a preliminary transport roller 107 and a preliminary transport pressure plate 108, are separated one by one by a separating piece 109 and a separating roller 110, and are transported to the reading position 113 of the image reading portion 102 by a pair of sheet feeding rollers 111 and 112. The document P1 transported to the reading position 113 is transported by a platen roller 114 while being brought into close contact with the document glass stand 105. At this time, the image reading portion 102 reads the image of the document P1 transported by the document feeding portion 103 by the reading sensor 104 stopped from moving at the reading position 113. The document P1 after read is discharged onto a document discharge tray 117 by a pair of sheet discharging rollers 115 and 116.
The “fixed-reading mode” will now be described. On the document glass stand 105, there is provided an index 118 which becomes placement indicating means when a document P2 is placed on the document glass stand 105 in the case of the “fixed-reading mode”. The index 118 is disposed on the right of the reading position 113 during the flow reading. The document P2 is placed on the document glass stand 105 with its left end abutted against the index 118. The image reading portion 102 reads the document placed on the document glass stand 105 while the reading sensor 104 is moved in the directions of double-headed arrow A by a driving mechanism, not shown. The document P2 placed on the document glass stand 105 is pressed against the document glass stand 105 by the pressure plate 119 of the document feeding portion 103 so as not to float.
As described above, in the image forming apparatus according to the first conventional example, the position for reading the image differs between the “flow-reading mode” and the “fixed-reading mode”. Accordingly, the image forming apparatus according to the first conventional example, as shown in FIG. 11, requires at a minimum a width corresponding to the length L1 of a document of a maximum size, plus an amount L2 corresponding to the width of the index 118 on the left side, plus an amount L3 corresponding to a width for securing the reading position 113 during the “flow-reading mode” further on the left thereof, and has been difficult in achieving the downsizing of the apparatus.
(The Image Forming Apparatus According to the Second Conventional Example)
So, like the image forming apparatus 200 according to the second conventional example shown in FIG. 13, there is one in which the reading position during the “flow-reading mode” is disposed on the right of the image reading portion. The image forming apparatus 200 according to the second conventional example is provided with an image forming portion A, an image reading portion B and a document feeding portion C. The image reading portion B and the document feeding portion C together constitute an image reading apparatus E.
This image reading portion B is also adapted to read a document by the fixed-reading mode and the flow-reading mode. The image reading portion B has a scanning rail 282 disposed toward the right and left on a frame 281. The image reading portion B is designed such that a document reading sensor 283, e.g. a contact image sensor (CIS) scans on the scanning rail 282 in parallelism to a document glass stand 284, and reads a documents set on the document glass stand 284 (the fixed-reading mode).
The image reading portion B has an abutment portion 280 against which the leading edge portion (left side) of the documents are abutted when the document is set on the document glass stand 284. Also, the image reading portion B is adapted to stop the document reading sensor 283 at a reading position D, and read the documents supplied one by one from a document stacking tray 252 by the document feeding portion C and moved on the reading position in a sub-scanning direction (the flow-reading mode).
Description will now be made of the construction of the document feeding portion C in the image reading apparatus according to the second conventional example.
FIG. 14 is a front cross-sectional view of the document feeding portion C.
The document feeding portion C has the document stacking tray 252 for stacking the documents thereon with the image bearing surfaces thereof facing downward, a pickup roller 203 at a location opposed to the documents, and a separating portion comprising a pad 204 and a separating roller 205 downstream thereof. The pickup roller 203 is rotatably provided on sheet feeding arms 219 and 220 (220 being not shown) pivotally provided on the rotation center shaft 201 of the separating roller 205. The pickup roller 203 is adapted to contact with the uppermost document (the last page) of the document stack placed with the images thereof facing downwardly.
Also, a document set sensor 244 is provided between the pickup roller 203 and the separating roller 205. The document set sensor is adapted to detect whether the documents are present on the document stacking tray 252. A pair of register rollers 206 and 207 are provided downstream of the separating roller 205. An ante-register sensor 245 is provided between the separating roller 205 and the pair of register rollers 206 and 207. The ante-register sensor 245 is provided to determine a transport amount for the separating roller 205 to transport the document to the pair of register rollers 206 and 207.
Downstream of the pair of register rollers 206 and 207, there is disposed a platen roller 208 for urging the document against the document glass stand 284 of the image reading portion B and at the same time, transporting the document. Downstream of the platen roller 208, there are disposed a pair of transporting rollers 209 and 210 for discharging the document on the document glass stand 284. Further downstream thereof, there are disposed a pair of sheet discharging rollers 211 and 212 for discharging the document to a discharge tray 218.
FIG. 15 is a top cross-sectional view of the image reading portion B and the document feeding portion C. As shown in FIG. 15, a hinge designated by the reference numeral 262 is provided leftwardly rearwardly of the image reading portion B and the document feeding portion C. A hinge denoted by the reference numeral 263 is rightwardly rearwardly of the image reading portion B and the document feeding portion C.
As shown in FIG. 16, the platen roller 208 has its front and rear ends mounted on pivotally movable arms 248 and 249, and are adapted to be rotated about the bearing portions 248b and 249b of the front and rear pivotally movable arms 248 and 249, respectively. The front and rear pivotally movable arms 248 and 249 are pivotally movable about the bearing portions 248a and 249a, respectively, and the opposite ends of the platen roller 208 are adapted to be independently pivotally moved with the pivotally movable arms 248 and 249. Also, the lowermost portions 248c and 249c (not shown) of the front and rear pivotally movable arms 248 and 249, respectively, are adapted to be reliably installed on the document glass stand 284.
Also, as shown in FIG. 14, the document feeding portion C has a pressure plate 255 for pressing the documents on the document glass stand 284 during the fixed-reading mode. The pressure plate 255 is comprised of an overlying elastic member 255a such as a sponge and an underlying white sheet portion 255b stuck on each other. When the document feeding portion C is closed, the white sheet portion 255b is installed on the documents on the document glass stand 284, whereafter the elastic member 255a is compressed until rubber feet 264, 265 and 266 are installed on the image reading portion B. Accordingly, the document on the document glass stand 284 is reliably pressed against the document glass stand 284 so as not to move from its placed position.
Also, the platen roller 208 is designed such that the front and rear ends thereof are independently grounded to the document glass stand 284 by the pivotally movable arms 248 and 249 and therefore, even if the grounded state of the document feeding portion C somewhat differs due to the dimensional error between respective mechanisms, the platen roller can be grounded to the document glass stand 284 in a constant state in the reading portion and therefore, it never happens that a fogged image is caused by the platen roller 208 floating from the document glass stand 284 more than a predetermined amount, and reading can be accomplished reliably.
In the above-described image forming apparatus 200 according to the second conventional example shown in FIG. 13, the reading position D is disposed on the right of the image reading portion B. Accordingly, the image forming apparatus 200 according to the second conventional example, unlike the image forming apparatus 100 according to the first conventional example, the abutment portion 280 can be disposed at the left end without the index 118 being disposed between the reading position during the flow-reading mode and the reading position during the fixed-reading mode and therefore, the document glass stand 284 can be made small.
Also, in the image forming apparatus 200 according to the second conventional example, as shown in FIG. 15, the document glass stand 284 is further downsized in such a manner that during the fixed-reading mode, the platen roller 208 presses the trailing edges of documents of a maximum size (LGL size in the present conventional example), thereby achieving the downsizing of the image reading portion B. Even if design is made such that the trailing edges of the LGL documents P2 (documents of the maximum size) are pressed not by the pressure plate 255 but by the platen roller 208, the platen roller 208 is pressed against the document glass stand 284 and therefore, the floating of the trailing edges of the LGL documents is prevented and a fogged image does not occur, and the reading of the documents can be accomplished reliably.
The platen roller 208, however, is designed such that the front and rear ends thereof are independently grounded to the document glass stand 284 by the pivotally movable arms 248 and 249 and therefore, when the document feeding portion C is opened, as shown in FIG. 17, the platen roller 208 is adapted to be pulled down from its broken-line position to its solid-line position by gravity and the pulling forces of biasing springs 253 and 254.
Also, in a state wherein the pressure plate 255 is closed, the elastic member 255a is compressed and crushed, but when the document feeding portion C is opened, the platen roller 208 is lowered to its solid-line position and becomes located by a distance “h” below the underside of the white sheet portion 255b of the pressure plate 255. When in this state, the LGL documents (of the maximum size) are placed and the document feeding portion C is closed, the platen roller 208 earlier contacts with the trailing edge portions (right end portions) of the LGL documents, whereafter the pressure plate 255 presses the documents.
When the documents are pressed against the document glass stand 284 by the pressure plate 255 (see FIG. 17) while the document feeding portion C is being closed as shown in FIG. 18, the pressure plate 255 comes into contact with the documents from the inner part thereof near to the hinges 262 and 263 which are the center of pivotal movement, whereafter the front side thereof comes into contact with the documents and therefore, before the front side (the pivotally movable arm 248) of the platen roller 208 contacts with the document glass stand 284, the pivotally movable arm 249 is pivotally moved in the direction indicated by the arrow Y, and when viewed from the front, is pivotally moved in the direction indicated by the arrow X indicated in FIG. 17. Accordingly, as shown in FIG. 19, the trailing edges of the documents of the maximum size positionally deviate in the direction indicated by the arrow X with the pivotal movement of the inner part of the platen roller 208.
The document feeding portion C is further closed and at a point of time whereat the pressure plate 255 has contacted with the documents, the pressure plate 255 presses the documents, which thus stop on the document glass stand 284 with their inner part deviated to the right. When at this document position, an image is read by the “fixed-reading mode”, the documents are placed on the document glass stand 284 while being rotated by an angle α, and this also gives rise to the problem that an output image is rotated by the angle α.
Also, even in a construction wherein document abutting means is present on the inner side, the documents (particularly thin paper) are strongly urged against the document abutting means, and this has given rise to the problem that the documents are buckled or damaged and a faulty output image occurs.